Various methods have been proposed for the formation of a metal film on a substrate in the conventional manufacture of an electronic component.
Patent Literature 1 (Japanese Patent Application Laid-Open No. 2006-52101) discloses, as a prior art, the enhancement of the adhesion between a substrate and a metal coating in which concavities and convexities are formed on the substrate surface with surface roughening treatment and the concavities are occupied with the metal. Patent Literature 1 discloses a method of preparing a metal coating by plating onto a metal coated ceramic substrate without use of the surface roughening treatment. The method includes a step of applying fine powders of at least two metals and/or metal oxides selected from a specified group of metal elements to a ceramic substrate surface, a step of strongly fixing the fine powders to the substrate surface using thermal treatment at 200° C. to 500° C., and a step of depositing a metal coating onto the substrate surface using the fixed fine powders as a seed layer.
Patent Literature 2 (Japanese Patent Application Laid-Open No. 2005-12200) discloses a piezoelectric/electrostrictive element including a body configured from ceramic, and an operation member having a lower electrode, a piezoelectric/electrostrictive film and an upper electrode. Patent Literature 2 discloses that inclusion of titanium in the body enables a reduction in sintering stress caused by thermal treatment between the body and the operation member, and then a large displacement is obtained.
The following problems are associated with metal coatings formed using the conventional method.
Firstly, when a ceramic layer is additionally provided over a metal coating formed on a ceramic substrate, after applying the ceramic material on the metal coating, high-temperature thermal treatment may be applied at a temperature which is greater than or equal to the particle growth initiating temperature for the particles forming the metal coating (for example, when the metal coating is made of Pt, the particle growth initiating temperature is in the vicinity of 750° C.). This type of high-temperature thermal treatment may reduce the surface smoothness due to a metal dome formation by expanding the metal film, or may reduce areas covered by the plated film due to partially breaking of the metal dome.